This relates to sensors and, more particularly, to ambient light sensors for electronic devices.
Cellular telephones and other portable devices with displays such a tablet computers sometimes contain ambient light sensors. An ambient light sensor can detect when a portable device is in a bright light environment. For example, an ambient light sensor can detect when a portable device is exposed to direct sunlight. When bright light is detected, the portable device can automatically increase the brightness level of the display to ensure that images on the display remain visible and are not obscured by the presence of the bright light. In dark surroundings, the display brightness level can be reduced to save power and provide a comfortable reading environment.
With conventional devices, ambient light sensors are implemented using first and second silicon photosensors to receive ambient light. The first photosensor is used to detect an amount of infrared light in the ambient light, whereas the second photosensor is used to detect an amount of visible light and infrared light in the ambient light. Readings from the first and second photosensors are subtracted to obtain a corresponding visible light level. This visible light level is then used to increase or decrease the display brightness level accordingly.
Computing visible light levels in this way, however, requires the infrared sensing capabilities of the first and second photosensors to be accurate and consistent relative to one another. Any mismatch in infrared sensitivity can cause the visible light reading to be erroneous. Designing and manufacturing two silicon photosensors that are well-matched in performance may be challenging.
It would therefore be desirable to be able to provide improved ambient light sensor systems for electronic devices.